1. Field of the Invention
The present invention relates to the storage of document information on a video disc and, more particularly, to a video disc and apparatus for providing hard copy reproduction of stored document information.
2. Description Relative to the Prior Art
It is generally known in the art to record video program material, on a video disc, according to a circular or spiral record track configuration with one frame being recorded per disc revolution. During recording and playback, the disc spins at a rate corresponding to the TV frame repetition rate which, in the United States, is 1800 per minute. Such recording configurations provide satisfactory results when recording subject matter having a large number of sequential frames, such as in a typical video program. For these applications, a spiral record track is most common. Suitable playback optics track the spiral record track in order to reproduce the thousands of frames which constitute the program material. A circular record track configuration can also be used in the recording of video program material, but such configuration suffers from the disadvantage that the playback optics must "step" from track to track during recording and playback. Such stepping is usually accomplished during the vertical blanking interval to avoid interference with the recorded program material.
Video discs are becoming increasingly important in applications involving the storage of document information (hereinafter sometimes called "document storage") because discs offer several advantages over microfilm systems. Assuming that each document, for example a bank check, is recorded as one 525-line frame of video information, present video technology potentially allows 54,000 documents to be stored on one side of a twelve inch diameter video disc (i.e. when one 525-line frame corresponds to one revolution of the disc). Further, because video discs are optically scanned, a random access system is practical wherein any one of the 54,000 documents stored on the disc could be located and displayed in seconds. It is apparent that the video disc represents a potentially valuable medium for document storage applications.
There are certain problems peculiar to document storage, however, which inhibit the application of video discs in this field. The resolution requirements for document storage applications are significantly greater than the already stringent requirements for conventional program material such as movies, etc. This more stringent resolution requirement is the result of having to be able to clearly discern each letter, number, symbol, etc., on the stored document. For example, if the stored document is a bank check, it is necessary to be able to read clearly not only the amount of the check and the signature, but also the account number (which frequently includes symbols) and the bank number. To complicate matters, many of the letter, numbers and symbols are similar in appearance.
Another problem involved in document storage on a disc is that it is often desired to make a hard copy reproduction of the stored document. A displayed video frame generally comprises two interlaced fields, yet the fields are recorded sequentially on the disc, i.e., field one is recorded and then field two is recorded. Upon playback through a video monitor, therefore, field one is reproduced and then field two. Most printers, however, print line-by-line starting at the top of the page and proceeding to the bottom. It would require substantial modification to the printer to make it compatible with a field sequential reproduction format. At the very least, the printer would have to be modified to start at the top of a page and print the lines of field one (lines 1, 3, 5 . . .) ending at the bottom of the page, and then return to the top of the page and print the lines of field two (lines 2, 4, 6 . . .) properly interlaced with those of field one. Such action would probably seriously impair the production rate (documents/hour) of the printer.